偏流板距离对亚声速射流冲击宽频噪声特性的影响

Broadband noise performance of subsonic jet with different impingement distances to a deflector

通过全消声室实验研究了不同冲击距离(L)下亚声速射流宽频噪声特性。利用远场传声器获得L=30D~2D(D为喷口直径)的噪声数据,并详细分析了频谱特性。试验结果表明,减小冲击距离:(1)上游所有频段的噪声都明显上升,极角α=120°总声压级(OASPL)在L<10D时增加了10~17 dB;(2)下游α=30°的噪声能量向低频转移,且频谱在L<10D时变化不明显;(3)偏流板产生噪声的中、高频段对边线影响较小,α=90°的频谱迅速衰减,在L<10D时形成陡峭的峰值。研究证实在噪声最强的方向(α=120°),随冲击距离的减小偏流板贡献的噪声功率占比呈线性增加。冲击距离小于势流核时,偏流板贡献大部分噪声能量,L=7D~5D时占比超过80%。另外射流冲击产生的噪声指向性明显,冲击噪声和后缘分离噪声在不同方向取得主导地位,相应频谱分别在上游和下游呈现高频主导和低频占优的特性。

To study the broadband noise characteristics of jet impingement on defector with different impact distances,an experimental study is carried out by using far-field microphones in a full anechoic chamber.Comprehensive data of the nozzle-plate distance(L)range between 30D(D is the diameter of nozzle exit)and 2D are obtained and the spectral characteristics are discussed.Reducing the impact distance,the results indicate:(1)The spectra increase significantly in all frequency bands,leading to an increment of the overall sound pressure level by 10–17 dB in the direction of polar angles(α)ofα=120°when L<10D;(2)The noise energy of downstream directions transfers to lower frequency and the spectra ofα=30°tend to collapse at different impingement distances when L<10D;(3)Since medium and high frequency impingement noise has a little effect on the sideline directions,the spectra of polar angle of 90°attenuate rapidly which form a steep peak when L<10D.The quantitative analysis prove that the proportion of sound power of defector increases linearly with the decrease of L in the direction of strongest noise(α=120°).Most noise are produced by deflector for impingement distance less than the length of potential core,such as 80%at L=7D–5D.Moreover,the directivity of deflector noise is obvious.Impingement noise or trailing edge separation noise is dominated in different directions.Correspondingly,the low frequency and high frequency noise plays a dominant role in the upstream and downstream directions respectively.